I'll answer my own post here. Managed to get it working after some tinkering. This is quite a dirty solution, as it always sends from the requested position to the end of the file (although no browser I've tried so far tries to set the range end to anything but the end of the file), doesn't respect ranges other than bytes, and so on.. Also just freshly copied from my test file, could probably use a lot of cleanup. But it least it works for seeking in streams:

	// Provide a streaming file with support for scrubbing
	private function streamFile( $contentType, $path ) {
		$fullsize = filesize($path);
		$size = $fullsize;
		$stream = fopen($path, "r");
		$response_code = 200;
		$headers = array("Content-type" => $contentType);
		
		// Check for request for part of the stream
		$range = Request::header('Range');
		if($range != null) {
			$eqPos = strpos($range, "=");
			$toPos = strpos($range, "-");
			$unit = substr($range, 0, $eqPos);
			$start = intval(substr($range, $eqPos+1, $toPos));
			$success = fseek($stream, $start);
			if($success == 0) {
				$size = $fullsize - $start;
				$response_code = 206;
				$headers["Accept-Ranges"] = $unit;
				$headers["Content-Range"] = $unit . " " . $start . "-" . ($fullsize-1) . "/" . $fullsize;
			}
		}
		
		$headers["Content-Length"] = $size;

		return Response::stream(function () use ($stream) {
			fpassthru($stream);
		}, $response_code, $headers);
	}

Then in the controller simply call something like

	return $this->streamFile("video/mp4", $path_to_file);

Hope it can help someone else looking for the same thing! By the way, some function like this would be a welcome addition to the Response class.

EDIT: Updated function with a small bugfix, sorry for bumping.